This invention relates to microwave power combiners and methods for qualifying diodes for use therein. One power combiner with which the disclosed method may be used is described, for example, in U.S. Pat. No. 4,121,174. Basically, it includes a central cavity with a plurality of negative resistance diode oscillator circuits spaced around the perimeter. Each of the oscillator circuits furnish electromagnetic energy to the cavity. And the combined energy is taped off by a probe that is inserted into the cavity.
A problem that exists in the prior art, with which the disclosed invention is concerned, is that of determining how to qualify diodes for simultaneous use in the combiner. In the past, the diodes were tested by their manufacturers via circuits that were substantially different from the power combiner in which the diodes were eventually to be used. These circuits typically were co-axial circuits with a low Q and without any resonating cavity. Thus, it is reasonable to expect that the tests were not sufficient to determine which diodes would operate best in power combiners that had resonating cavities and a high Q.
The testing problem is complicated by the fact that diodes cannot simply be individually inserted into the power combiner with which they are to be used and there be tested one at a time. This is because the electrical impedance which each diode sees in the power combiner is dependent upon the total number of diode oscillators that are active. Thus, a diode which performs well in an individually activated oscillator circuit of a power combiner, still might not perform well when operated in parallel with all of the other oscillator circuits in the combiner.
Therefore, it is a primary object of the invention to provide a method of testing diodes for determining which of them will perform well in combination in a microwave power combiner.